A lens which is mounted on a monitoring camera, an on-vehicle camera and a camera for a portable apparatus is required to have a viewing angle of 90 degrees or more and to reduce its aberration so as to attain sufficient resolution. Further, the lens is also required that the number of lenses is suppressed to a minimum from the standpoint of cost. Therefore, a lens has been proposed which is constituted to be three lenses in three groups and in which the ratio of focal lengths and the ratio of Abbe numbers of the respective lenses are set in predetermined conditions (see Japanese Patent No. 4268323).
However, it is required that the “F”-value indicating brightness of the entire lens system and a level of aberration are further reduced in comparison with the wide-angle lens described in the above-mentioned Patent Literature.